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<br /> TABU CHECKLIST-Ot REQUIRED D
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Nasse and Locat'som Exxon RAS#7-0137, 1605 South El Dorado Street, Stockton, San Joaquin County
<br /> Two irrigation water supply wells are approximately
<br /> 1. Distance to production wells for municipal, domestic, agriculture, 1,320 feet southwest of the site. Well construction
<br /> industry and other uses within 2000 feet of the site; details were not submitted.
<br /> Three USTs were removed in
<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, 1992,Three
<br /> one UST was
<br /> excavation contour's and sample locations, boring and monitoring well elevation contours, installed in 1993. Site maps
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; are provided.
<br /> y" Boring logs and cross-sections show silty clay
<br /> 0 3. Figures depicting lithology(cross section), treatment system.diagrams; and silty sand.
<br /> Approximately 300 cubic yards of soil were excavated
<br /> 4. Stockpiled soil,remaining on-site or off-site disposal(quantity); and used as backfill on-site. "
<br /> I
<br /> 5. Monitoring wells remaining on-site, fate; Seven monitoring and two SVE wells currently exist on-site. The wells will be
<br /> 0 properly destroyed pending site closure. LL
<br /> dwater levels vary from 23 to 48 feel elo,
<br /> Groun
<br /> 6. Tabulated results of all groundwater elevations and depths to water, ground surface, and flow has varied from northeast
<br /> to southeast.
<br /> 7. Tabulated results of all sampling and analyses: December 2000 maximum groundwater monitoring results show MtBE
<br /> at 10 pg/l in SVE well VEW2 at the south end of the former tank pit.
<br /> Detection limits for confirmation sampling All other constituents were non-detect Confirmation groundwater
<br /> Lead anal ses samples collected in 8/99 near the former USTs show TPHg and WE
<br /> y respectively. Benzene was non-detect.
<br /> /1 and 19.6 /!
<br /> 0 at 3,930.}►g pg1l,
<br /> 0 8. Concentration contours of contaminants found and those remaining in soil Lateral and vertical extent of soil and
<br /> and groundwater, and both on-site and off-site: groundwater contamination is defined.
<br /> Lateral and Vertical extent of soil contamination
<br /> Lateral and Vertical extent of groundwater contamination
<br /> 9: Zoe of influencep
<br /> calculated and assumptions used for subsurface An SVE system was operated at the site
<br /> Zone
<br /> 0 remediation system and the zone of capture attained for the soil and from11195 to 3/96 and from 2/97 to 4/98.
<br /> Consultant estimates that 1,551 pounds of
<br /> groundwater remediation system;
<br /> TPHg was removed from site soils.
<br /> F1 10.Reports/information IT1 Unauthorized Release Form El QMRs(7/91 to 12/00)
<br /> 0 Boring logs El PAR FRP Other(Confirm. Soil Boring Results& Closure, 11/00)
<br /> 11.Best Available Technology(BAT) used or an explanation for not using BAT; Remove contaminate source, remedlation
<br /> Y by SVE, verification_ monitoring.
<br /> 2.-Reasons why;background was/is -
<br /> unattainable using BATTPHg, BTEX, and MtBE remain in on-site soil and groundwater.
<br /> 13.Mass balance calculation of substance A mass balance was not completed. Consultant states that 1,551 pounds of
<br /> treated versus that remaining; TPHg was removed from site soils. Results of confirmation sampling show 50
<br /> to 90 percent of initial contamination has been remediated.
<br /> A Tier 1 RBCA was completed for the site. Consultant
<br /> 0 Y 14.Assumptions,parameters, calculations and model used in risk states that constituents remaining in soil and
<br /> assessments, and fate and transport modeling; groundwater do not pose a significant risk to occupants.
<br /> 15. Rationale why conditions remaining at site will not adversely Consultant states that given the relatively low
<br /> T� impact water quality, health, or other beneficial uses;and concentrations of remaining contamination,the potential
<br /> for off-site migration of chemicals at measurable levels
<br /> is considered minimal.
<br /> By- Comments: The site is currently an active service station. Three 10,000-gallon gasoline USTs were removed from the
<br /> site in 1992, and one 20,000 gallon UST was installed in 1993. Soil contamination was identified during the tank removal,
<br /> and multiple borings, seven monitoring and two SVE wells were installed. An SVE system operated intermittently from
<br /> 11/95 to 4/98, and approximately 1,551 pounds of TPHg was removed. Confirmation soil and groundwater samples
<br /> Date: collected in 8/99 show remaining contamination is limited to an area around the former UST tank pit. The site is paved
<br /> with asphalt, which should limit further leaching and transport of contaminants. Based on the complete site
<br /> �I /0characterization, remediation, and verification monitoring completed to date, Board staff concur with San Joaquin
<br /> ii County's closure recommendation.
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